Electric fuse-link,particularly for outdoor use



Aug. 4, 1970 F. c. E. TAPLIN EFAL 3,522,571

I ELECTRIC FUSE-LINK, PARTICULARLY FOR OUTDOOR USE Filed Jan. 30, 1969 12 Sheets-Sheet 1 M/VENTDRS Fmcns cYku. 6470M TAPLIA/ Tum Rmmu Am! IArms/Viv:

ELECTRIC FUSE-LINK, PARTICULARLY FOR OUTDOOR USE Filed Jan. 30, 1969 g-19.70 F. c. E. TAPLIN ET AL 2 Sheets-Sheet 2 7 am WM 1 ABSTRACT OF THEDISCLOSURE A fuse-link in an insulative. fuse body, said link beingsecuredwbetween twoterminals enclosed in a first insulative tube, saidfirst insulative tube being secured. to a first terminal, a secondinsulative tube is secured to a second terminal said second tube beingfitted slidably over said first tube, whereby said second tube slips oifsaid first tube-when said fuse-link melts.

This invention relates to fuses for use in medium and high-voltagesystems, and more particularly to fuse-links for the electro-conductiveconnection of units of electric equipment g(.transformers,:circuit-breakers or the like) with a power transmission line or witheach other via another conductor of electricity.

Such fuses are normally made of a short length of a readily fusible,electrically conductive metal wire materialv designed tomelt when passedby a current of a predetermined intensity over a given-usually'briefperi0d of time. Particularly foruse in the open air, the fuse isfrequently arranged vertically, or substantially vertically, between twoterminals or: conductors which form part of the fuse-linkandhavecross-sections which considerably :exceed that of the fuse itself,the fuse being secured to theterminals in any suitable manner to ensurethe flow of current under normal conditions. a

In someqknown constructions thefuse is surrounded by atubeofinsulatingmaterial, which is attachedto one ofrthe terminals,,the,tube beingspaced from the fuse. The .-insu,lating tube limits the spread of fuseparticles when the fuse, melts which often occurs-explosively. Moreover,it limits the spread of the arc and may also contribute to the coolingof these particlesbut, as a rule not toan adequate extent.- a l 1 i Inexpulsion fuses such as are used in the open, the tube .is mounted as arule on a terminal arranged at a higher level, its openend surroundingthe lower terminal, and, meansare often provided either in closeassociation withflth e fuse, or externally, thereof, to secure a rapidseparation of the terminals after the melting of the fuse for thepurpose of increasing the length of the arc. The are causes arapid riseof the temperature of the air or gas contained in'the tube which,consequently expands towards the open tube end and assists the expulsionfrom the tube of the movable terminal attached to the lower conductor.With the air or gas, and the terminals, however, also the molten fusemetalis expelled, at least partly in the form of liquid particles whichmay be extremely hot'or incandescent. Y

If the current is grossly excessive, the fuse metal may be completelyevaporated, but under most conditions incandescent metal particles areproduced which may reach the ground in that condition and may,therefore, cause ignition of combustible material on the ground andthereby give rise to bushfires, grass fires and other fire damage,

"ice

particularly in dry weather or under unfavourable conditions.

The object of the present invention is to provide a fuselinkconstruction suitable for use in high and mediumhigh voltage systems andmore particularly for use in the open air, or otherwise under conditionsinvolving fire danger, the fuse-link being constructed and designed toexclude, or at least very considerably reduce, the likelihood ofexpulsion therefrom of incandescent fuse material which could reach theground in a dangerously hot condition.

. According to the invention this is achieved by providing means whichcause the expulsion of the fuse material to berestrained and/or delayed,and any molten fuse material to be deflected away from combustiblematerial.

In the fuse-link according to the invention the fuse wire securedbetween two terminals in the system to be protected, is enclosed withina tube or sleeve-hereinafter called the first tube-of highlyheat-resistant, electrically non-conductive material secured to one ofsaid terminals, with no or only little space between the fuse proper andthe inner wall of said tube, the fuse-link in cluding at least onefurther tube or sleeve of highly heatresistant, electricallynon-conductive material-hereinafter called the second tube-which issecured to the second terminal and, being a sliding fit on said firsttube,

- is slidably displaceable along the latter, the second terminal beingconnected to a flexible conductor for attachment to an appliance,apparatus or the like to be protected by the fuse-link from overload.The second tube or sleeve which surrounds the first tube over asubstantial part of the length of the latter, thus can slip olf thefirst tube when the fuse melts, and then drop down from the fuse-link bygravity and/ or spring action, or otherwise.

In a preferred embodiment of the invention the second tube or sleeve isa sliding fit, and is thus slidably displaceable, within a third tubesecured to the first mentioned terminal, the length of said third tubebeing such that the second tube is still in part accommodated thereinafter having been displaced past the first tube. In that case, s12 1cms12 oqn; tsrg our urqtrm popuedxo sJnodeA snoesafi hot or glowing metalparticles entering the space surrounded by the third tube are notimmediately discharged to the ambient atmosphere after the second tubehas been detached from the first tube, but are first made to enter I thespace between the first and third tubes in a direction towards the firstterminal, and are allowed to escape into the atmosphere only after thesecond tube has been detached from the third tube, whereby the escape ofthe gases and vapours as well as of any liquefied metal from i thefuse-link into the atmosphere is still further delayed so that thedanger of ignition of combustible material such as dry leaves, twigs,etc. lying on the ground is practically eliminated.

If so desired an additional tube of heat-resistant material may beaccommodated within the abovementioned form of liquid particles, is verysmall. It is assumed that the very high pressure developed within thetube or sleeve which closely surrounds the fuse material, effects theelimination and rapid suppression of the arc produced therein when thefused material is vapourised. The very high temperature within thatinnermost tube under such conditions material. The metal vapour whicheventually escapes into the atmosphere is cooled so effectively that itscontents cannot cause any fire danger. Any glowing or incandescent fuseparticles leaving the open end of the first tube or sleeve at an earlystage are expelled and are made to impinge upon the inner wall of saidsecond tube on which they are cooled so that they are not likely to bedangerously hot when they flow out from that tube after it is detachedfrom the fuse-link.

For very high voltages, e.g. of 10,000 v. or more, the duration of thearc may be too long for effecting a sufiiciently rapid cooling of thevapours and it is in this case that the provision of a third outer tubeis of particular advantage, as the third tube will cause a further delayin the discharge of the gas, metal vapour or vapours and of liquidparticles, if any, into the surrounding atmosphere.

In order to more particularly describe the invention, reference is madeto the accompanying drawings wherein:

FIGS. 1 to 3 are views showing, by way of example only, the generalarrangement of a disconnecting switch, in four successive phases of itsoperation, in which the fuse-link according to the invention may beused, the switch being shown as connected between a power transmission!line and a consumer unit, e.g. a transformer.

FIG. 4 shows diagrammatically in longitudinal section an embodiment ofthe fuse-link according to the invention suitable for higher voltages,e.g. voltages of 10,000 v. or more.

FIG. 5 shows, likewise diagrammatically and in longitudinal section,another embodiment of the fuse-link suitable for medium and lowervoltages.

The disconnecting switch shown in FIGS. 1 to 3 comprises a tubularbridge made of insulating material for attachment between two resilientelectro-conductive elements 11 and 12 which are secured to the oppositeends of an insulator 13. The element 11 is provided with a terminal 14suitable for attachment to a conductor 15 and by suitable clamping means16, e.g. to a power transmission line 17. Similarly, the resilientelement 12 is provided with a terminal 18 suitable for attachment by aconductor 19 to a terminal of an electrical apparatus or unit, e.g. atransformer 20, circuit-breaker or the like. The insulator 13 of theconnecting switch may be fastened, for instance, to a part 21 of a mastor tower of a transmission line by means of a bracket structure 22 and aloop or ring 23.

The arrangement of the bridge 10 is either vertical or substantiallyvertical as shown, the lower end of the bridge being secured to thelower end 24 of the insulator 13 for instance by a detachable hingestructure 25 which includes a bell-crank lever 26 on a hinge-pin 27. Afuse conductor 28 is attached to the lever 26 and extends into thetubular bridge 10 to the required extent.

The upper end portion 29' of the bridge is provided with a knob 30 whichnormally engages a recess 31 provided at the free end of the resilientelement 11, the knob 30 being detachable, e.g. manually with the aid ofa properly insulated rod and hook (not shown) when the latter is made toengage in a ring 32 which forms a part of the upper bridge end portion29 and pull is exerted on the ring by an operator.

The disconnecting switch illustrated in FIGS. 1 to 3 represents only aspecific embodiment of a device which can be fitted with a fuse-linkaccording to this invention, the fuse-link being accommodated in thetubular bridge 10 of the switch. In this case the break of the switchcan also be effected by an overload in the connection or phase betweenthe transmission line 17 and the unit, e.g. a transformer 20 fed fromthe line 17, due to the action of the fuse-link which serves forprotecting the apparatus or a phase of the latter.

FIG. 4 shows an embodiment of a fuse-link suitable, for instance, for avoltage of 10,000 to 12,000 v. or

V 4 I 3 more within the bridge 10*. The fuse-link comprises two tubularelectro-conductive contact elements 36 and 37 in mutual alignment. Thecontact element is a tight fit in a blind bore 38 formed centrally in aterminal 39 which may be the upper terminal of the fuse-linkaccommodated within the upper part 29 of the bridge 10. The tubularcontact element 37 which is arranged at a distance from the element 36,is rigidly fitted into an end portion of a ferrule 40, the opposite(lower) end portion of which clampingly retains the dropout conductor 28which in FIGS. 1 to 3 is illustrated in different positions relative tothe bridge 10.

A first insulation tube 42 of highly heat-resistant and non-inflammablematerial such as polytetrafiuorethylene (e.g. that sold under theregistered trademark Teflon) or horn fibre, is rigidly secured to thecontact element 36, and to the terminal 39. A thin high-tensile wire 43,e.g. a steel wire, is anchored to the elements 36 and 37. At least onefuse wire 44 of a required current carrying capacity is secured togetherwith the steel wire 43 at two distant points between the tubular contactelements 36 and 37. The fuse wire 44 extends parallel to the steel wire43 which in this embodiment acts mainly as a mechanical reinforcementwithin a hollow space 45 which, if so desired, may be bounded orrestricted by a narrower insulating tube 46 disposed between the ends 47and 48 of the tubular contacts 36, 37 which face one another within theinsulating tube 42. The fixation of both the fuse wire or wires 44 andthe steel wire 43 is effected by squeezing the wires together within thetubular contact elements, e.g. at 49.

A second insulating tube 50, which is likewise highly heat-resistant andnon-inflammable, consisting for instance also of Teflon, is rigidlysecured to the ferrule 40 by a collar or bandage 51. y

The second tube 50 which in the normal operational condition of thefuse-link extends over at least a part of the length of the first tube42,- is slidably displaceable on the latter so that, if by an overloadthe fuse wire or wires 44 and, consequently, also the steel wire 43 arecaused to melt and/or to be vapourised, the air or gas and metalvapours, if any, contained in the space 45 expand rapidly and the secondtube 50 is displaced along the first tube until it is completelydetached therefrom.

A still further or third insulating tube 52 of the same or of a similarheat-resistant and non-inflammable material is secured to the terminal39. In the operative condition of the fuse-link this third tube extendsover the full length of the first tube 42 and also over most of thelength of the second tube 50 so that the latter, which is slidablydisplaceable within the third tube 52, is practically completely encasedtherein. There is an annular space 53 between the first tube 42 and thethird tube 52 in which the second tube 50 is slidingly accommodated.

If after the melting of the fuse wire or wires 44 and the steel wire 43the second tube 50 has overshot the (lower) end 54 of the first tube 42,the spaces 45 and 53 are interconnected so that expanding gases andvapours have the tendency now to continue their expansion into the space53, the direction of their flow to be partly reversed, and the ejectionof atomised and/ or liquid fuse particles to be slightly delayed untilin the course of the further displacement of the second tube caused bythe expansion of the gas the tube 50 is entirely expelled from the open(lower) end 55 of the third tube 52. An insulating ring 56 fitted in thespace 53 between the insulating tubes 42 and 52 close to the terminal39, prevents contact between the latter and the hot metal vapours of thearc.

During the total period of expulsion the hot metal particles pass theinitially cool inner walls of the first, second and third tubes 42, 50and 52 so that they are themselves subjected to a strong cooling actionwhich is continued during the final drop of the metal particles to theground through the air. Consequently, such liquid or solid metalparticles as finally reach combustible material, e.g. on the ground areno longer likely to have an incendiary effect on such material.

The modified form of fuse-link illustrated in FIG. in which the samereference numerals denote the same parts, differs from that describedwith reference to FIG. 4 only by the omission of the third tube. In thisembodiment also the flow of the expanding gas and/ or vapour isdeflected and at least momentarily reversed after the second tube 50 haspassed the open (lower) end 54 of the first tube 42. The escape of hotmetal particles and vapour from the hollow space 45 and/ or from theinnermost tube 46 in the direction of the original expansion istherefore delayed, and cooling of this hot material intensified.

The fuse-link described with reference to FIG. 5 although not aseffective as that described in the first place, is nevertheless suitablefor use in systems employing medium or lower voltages, i.e. voltagesbelow 10,000 v.

The fuse-link according to the invention is capable of still furthermodification within the scope and ambit of the appended claims.

Thus, for instance, it is possible to use a fourth outer tube, orsleeve, in which the third tube is displaceable, if it is necessary toobtain a further deflection or change of direction in the flow of theexpanding gas and/or metal vapour.

In the embodiment shown and described it was assumed that the expandinggas and the hot metal particles tend to be expelled in a downwarddirection, e.g. toward the ground. It should be understood, however,that the device can also be arranged differently in space, if sorequired.

In the fuse-links described above, a high-tensile wire, e.g. a steelwire, is used for the purpose of mechanically reinforcing the fusiblesystem. The invention however, is also applicable to fuse-links which donot employ such a reinforcing wire. Moreover, it is within the scope ofinvention to use a high-tensile wire or wires alone as the fusiblematerial.

It should finally be noted that the values of voltages stated in theforegoing are only approximate values, as the capability of thefuse-link according to the invention of handling voltages of a givenmagnitude does not depend exclusively on the number of mutuallydisplaceable insulating tubes, but also on other factors which includethe lengths and other dimensions of these tubes, of the fuse wire orwires and/or the arrangement of the fuse-link relative to the groundand/or to other parts of a system.

What we claim is:

1. A fuse-link connected between two terminals in an electric system tobe protected against overload, said fuse-link comprising at least onefuse wire enclosed within a tube or sleeve of highly heat-resistant andelectrically non-conductive material-hereinafter called the firsttubethe first tube being secured to one of said terminals with little,if any, space between the fuse wire and the inner wall of said firsttube, and at least one further tube or sleeve of highly heat-resistantelectrically non-conductive material-hereinafter called the secondtube-said second tube being secured to the second of the two terminalsand being slidably displaceable along the first tube, said secondterminal being connected to a flexible conductor for attachment to aunit to be protected.

2. A fuse-link as claimed in claim 1 wherein said second tube isslidablydisplaceable within a still further tube or sleeve of highlyheat-resistant and electrically non-conductive material-hereinaftercalled the third tubethe said third tube being secured to thefirst-mentioned terminal concentrically to the first tube with suchclearance between the first and third tubes that the second tube can befreely displaced relative to the first and third tubes when the fusewire is broken, the length of the third tube being such that it projectsbeyond the free end of said first tube so that it accommodates at leasta part of the length of said second terminal when the fuse-link is inits operative condition.

3. A fuse-link as claimed in claim 1, wherein the second tube is asliding fit on the first tube.

4. A fuse-link as claimed in claim 2, wherein the second tube is asliding fit on the first tube and a sliding fit within the third tube.

5. A fuse-link as claimed in claim 1, wherein the fuse wire is held inposition within the first tube by two mutually spaced tubular contactelements, one of said contact elements being connected with saidfirst-mentioned terminal and secured to the said first tube, whereas theother contact element is conductively connected and rig idly secured tosaid second terminal and is displaceable within said first tube togetherwith said second terminal.

6. A fuse-link as claimed in claim 5, wherein the fuse wire is, or thefuse wires are secured to the said tubular contact elements by clampingsame into the end portions of said contact elements which face oneanother within the first tube.

7. A fuse-link as claimed in claim 5, wherein the said fuse Wire is, orthe fuse wires are clamped into the end portions of said tubular contactelements which face one another within the first tube, together with ahigh tensile wire adapted to act as a mechanical reinforcement for saidfuse wire or fuse wires.

8. A fuse-link as claimed in claim 5 wherein the said fuse wire isconstituted by a steel or other high tensile wire.

9. A fuse-link as claimed in claim 1, wherein the said fuse wire is, orthe said fuse wires are encased within a further insulating tubeaccommodated within the said first tube between the said tubular contactelements.

10. A fuse-link as claimed in claim 2, wherein a ringlike body ofinsulating material is accommodated within the clearance between thesaid first and third tubes close to said first-mentioned terminal, saidring-like body preventing the establishment of electric contact betweenthe said terminal and hot metal vapours of an are within said clearance,in the event of an overload.

References Cited UNITED STATES PATENTS 2,749,408 6/1956 Billings337-248X 3,374,329 3/1968 Bronikowski 337203 X HIRAM B. GILSON, PrimaryExaminer US. Cl. X.R. 337

